1. Field of the Invention
The present invention relates to a bicycle front derailleur. More specifically the present invention relates to a bicycle front derailleur wherein a chain will not be caught by a chain entering edge of a movable member when the chain is oscillated wildly in an upward direction.
2. Description of the Prior Art
A conventional bicycle derailleur comprises, a shown in FIGS. 13, 14 and 15, a base member 4 fixed at a lower portion of a seat pipe 2 by mounting means such as a mounting band 3, a shift link mechanism 5 such as a pantograph mechanism, a movable member 6 supported by the shift link mechianism 5. The movable member 6 connects inner and outer guide plates 7 and 8 opposed to each other at a predetermined spacing. The movable member can be moved laterally of a bicycle by the shift link mechianism 5.
In this type of front derailleur, when a chain C is to be shifted from a smaller-diameter sprocket which is placed inward laterally of a bicycle to a greater-diameter sprocket which is placed outward laterally of the bicycle, a control lever is operated. The control lever action is transmitted, via a control cable T which includes an inner cable t1 and an outer sheath t2, to the shift link mechanism 5, which shifts the inner and outer guide plates 7, 8 outward laterally of the bicycle, causing an inner face 9 of the inner guide plate 7 to press the chain C outwardly to force a portion of the chain C to engage the greater-diameter sprocket adjacent to the sprocket presently engaged by the chain C. As the greater-diameter sprocket turns, the chain C is completely shifted to that greater-diameter sprocket.
On the other hand, to shift the chain C from an outward-located greater-diameter sprocket to an inward-located smaller-diameter sprocket, the shift link mechanism 5 is caused to move the pair of guide plates 7, 8 inward laterally of the bicycle. This causes an inner face 9 of the outer guide plate 8 to press the running chain C inwardly, forcing the chain C to move from the present sprocket down to the adjacent smaller-diameter sprocket.
As shown in FIG. 15, the chain C comprises alternating pairs of inner link plates 12 and outer link plates 13, and rollers R. Each of the rollers connect a pair of the inner link plates 12 opposed to each other at a predetermined spacing to an adjacent pair of the outer link plates 13 opposed to each other at a predetermined spacing. The chain C engages the sprocket in such a manner that spaces formed by each opposed pair of the inner link plates 12 and the outer link plates 13 are filled by teeth of a sprocket (not shown), whereas the rollers fit in spaces formed between the teeth of the sprocket. With this constitution, the chain C has different dimensions in its width, i.e. one represented by a distance between an opposed pair of the inner link plates, and another represented by a distance between an opposed pair of the outer link plates, with resulting step portions formed by a thickness of the outer link plate at areas where an outer link plate overlaps an adjacent inner link plate.
On the other hand, as shown in FIGS. 13 through 15, the movable member 6, which connects the inner and outer guide plates 7, 8, is often made integrally with the inner and outer guide plate 7, 8 by punching and pressing a thin plate of metal.
This type of conventional movable member 6 formed by punching and pressing methods is, as shown in FIG. 14, formed with a connecting portion 23 at its top portion, which integrally connects the pair of guide plates 7, 8 with a predetermined space therebetween, whereas a chain entering edge 14 of the movable member 6 is left as punched, with a cut plane 14a, without further machining. As a result, as shown by phantom lines in FIGS. 13 through 15, the chain is apt to be caught by the chain entering edge 14 at one of the step portions formed by the outer link plate 13.
Particularly, when a bicycle is running down on a steep hill of a rugged road condition, pedalling operation is sometimes stopped momentarily, leaving the chain C under no tension during that moment. This allows the chain C to be oscillated wildly in a vertical direction, sometimes with a portion of the chain C being whipped wildly upward so that an edge portion of the chain's outer link plate 13 rides on the chain entering edge 14 of the movable member 6, and is caught by it.
When the pedalling is resumed to tension the chain C, with the portion thereof still remain caught by the movable member, the chain C pulls the movable member 6, which is very likely to cause damage to the entire front derailleur.
In addition, the cut plane 14a of the the inner and outer guide plates 7, 8, which is part of the chain entering edge 14 is left as punched as mentioned hereinabove and therefore, is very sharp. As a result, the chain C may be damaged when it hits or contacts the cut plate 14a.